Sequencing Help - Urgent

I need help with this sequencing question :

A venetian blind consists of twentyfive slats, each 3mm think. When the blind is down, the gap between the top slat and the top of the blind is 27mm and the gap between adjacent slats is also 27mm, as shown in the first diagram.

When the blind is up, all the slats are stacked at the top with no gaps.

i) Shoow that when the blind is raised, the bottom slat rises 675mm
ii) how far does the next slat rise
iii) Explain briefly why the distances the slats rise an arithmetic sequence
iv) find the sum of all the distances that the slats rise when the blind is raised